Primary and secondary bushings are utilized in step-down transformers in distribution networks. Typically, a network transformer includes primary bushings, which electrically couple the fluid filled interior of the network transformer with high input voltage. Secondary bushings provide output terminals from the transformer tank to low voltage (480V and under) power cables. Generally, the secondary bushing is welded into the transformer wall via a metal flange. The transformer is typically filled with oil, which acts as an insulation medium between the internal components of the transformer. As a result, the secondary bushing is molded from epoxy in order to ensure an adequate seal that prevents the transformer oil from leaking out of the transformer tank. Typically, the connector positioned outside of the transformer wall has bare copper bus bars that extend out from the epoxy. Currently, power cables are connected to this copper bus via lugs, which results in exposed and energized copper. Under normal conditions the presence of exposed conductive connections is not an issue due to the low voltage (480V and under) present. Further, insulation of the exposed conductive contacts is not necessary, because the distance between the exposed contacts and ground plane is far enough that flashovers do not occur.
However, the exposed contacts can result in electrical failures in situations where the water level outside of the transformer rises to the point that all exposed copper is submerged. This is problematic especially in salt water, which is more electrically conductive. As a result, there are flashovers from the copper bus bar on the bushing back to the grounded wall of the transformer. This can eventually cause a phase to ground or phase to phase failure.
Various solutions attempt to prevent these failures by placing a seal over all the contacts of the secondary bushing. A problem with a seal that encompasses all of the contacts is that it allows an air space to be present between the conductive component and the sealing device. Further, these designs often do not provide a sufficient moisture seal, because they use one piece that attempts to seal to multiple cable connectors. As a result, if one seal is compromised due to irregularities with the cable or environmental restrictions (tight cable bend radius or contamination), all adjacent cable connectors are also compromised. In addition, the presence of water between the conductive components and the sealing device provides a pathway for water to contact with the cable connector terminal.
Therefore, there is a need in the art to insulate the conductive connectors of the cable connectors of the secondary bushing. This is preferably accomplished by coupling a sleeve composed of insulative material over the connection. Further, there is a need to create an individual water seal for each of the cable connectors. This design reduces the chances of failures by preventing any water from coming into direct contact with the bus bar and seals each of the cable connections individually.